1. Field
One embodiment of the present invention relates to a liquid droplet spraying apparatus for spraying liquid droplets from nozzles connected to pressure chambers by selectively applying spraying pressure to the pressure chambers storing liquid using an actuator.
2. Description of the Related Art
Conventionally, it is known an inkjet recording apparatus for carrying out recording on a recording medium using ink by scanning ahead unit for spraying ink droplets over the recording medium faced on the head unit. The head unit is provided with a plurality of pressure chambers for storing ink, common ink chambers for supplying ink to the respective pressure chambers, a piezoelectric actuator disposed adjacent to the respective pressure chambers, and a drive circuit for driving this piezoelectric actuator; the piezoelectric actuator driven using the drive circuit selectively applies spraying pressure to the pressure chambers so that ink droplets are sprayed to the recording medium from nozzles connected to the pressure chambers.
When spraying pressure is applied to the ink inside the pressure chamber using the piezoelectric actuator, the ink moves toward the nozzle and simultaneously tends to move from the pressure chamber to the ink supply side, that is, the upstream side. As the movement of the ink in a direction opposite to the spraying direction lowers spraying efficiency, such movement should be restricted as much as possible. After the ink droplets are sprayed, pressure inside the pressure chamber should be lowered so that excess ink is not sprayed.
Hence, conventionally, the pressure loss of the pressure chamber or the nozzles among the ink flow passages formed inside the head unit is made higher than those of the other sections so that the pressure inside the pressure chamber is lowered after ink spraying and so that stable ink droplets are discharged.
However, in the conventional methods described above, in order to obtain a sufficient pressure loss in the pressure chamber, an increased length or a very small cross-section area of the pressure chamber is required, thereby causing the following problems.
First, when the length of the pressure chamber is increased, the entire size of the head unit becomes larger, and the period of pressure fluctuation becomes longer. This results in a limitation in the speed of recording. Next, when the sectional area of the pressure chamber is made very small, larger pressure must be applied to the pressure chamber to obtain an ink droplet having a predetermined volume, and very large negative pressure is generated inside the pressure chamber. This impairs spraying stability. Furthermore, when the proportion of the pressure loss on the nozzle side is made higher, the proportion of the sprayed liquid droplet volume with respect to the generated pressure becomes smaller; as a result, the spraying speed rises excessively, and the meniscus inside the nozzle is liable to collapse.
For these reasons, a configuration has been devised conventionally in which the common ink chamber is connected to the pressure chamber using a narrowing portion serving as an ink passage. Since the narrowing portion has a pressure loss larger than those of the common liquid chamber and the pressure chamber, a sufficient pressure loss is obtained without increasing the length of the pressure chamber more than necessary and without making the sectional area of the pressure chamber very small in comparison with the conventional configuration. As a result, when pressure is applied to the ink inside the pressure chamber using a piezoelectric actuator, the flow of the ink toward the nozzle can be generated efficiently. Furthermore, after the ink is sprayed, the pressure inside the pressure chamber is lowered so that excess ink is prevented from being sprayed, whereby recording can be carried out with excellent spraying efficiency at high speed.